Dispersant having multifunctional head and phosphor paste composition comprising the same

ABSTRACT

Disclosed is a dispersant having a multifunctional head, and a phosphor paste composition comprising the dispersant. The dispersant has a multifunctional head that comprises an acidic group, a basic group and an aromatic group, thereby enhancing an affinity for the surface of phosphor particles and improving dispersibility.

CROSS REFERENCE TO RELATED APPLICATION

This application is a divisional of U.S. patent application Ser. No.11/852,734 filed on Sep. 10, 2007, the content of which in its entiretyis herein incorporated by reference.

BACKGROUND OF THE INVENTION

This non-provisional application claims priority under 35 U.S.C. §119(a)to Korean Patent Application No. 10-2007-0027591 filed on Mar. 21, 2007,the entire contents of which are hereby incorporated by reference.

Field of the Invention

The present invention relates to a dispersant having a multifunctionalhead and a phosphor paste composition comprising the dispersant. Morespecifically, the present invention relates to a dispersant having amultifunctional head that comprises an acidic group, a basic group andan aromatic group, thereby enhancing an affinity for the surfaces of avariety of phosphor particles and thus improving dispersibility.

Description of the Related Art

In recent years, a variety of display devices have been developed andwidely used as substitutes for cathode ray tubes (CRTs). Such displaydevices include flat panel displays (FPDs), such as, for example, liquidcrystal displays (LCDs), plasma display panels (PDPs),electro-luminescent displays (ELDs), field emission displays (FEDs), andvacuum fluorescent displays (VFDs). Such display devices can be used forexterior decorations or display parts of electronic appliances, e.g.,exterior decorations or keypads of cellular phones.

It is desirable for such display devices to include a fluorescentscreen. The luminescent properties of the display devices can be varieddepending upon the physical properties. In other words, although aphosphor inherently has a high luminance, unless a fluorescent film madeof the phosphor is suitably formed, the display device including thefluorescent film cannot exhibit high luminance.

A fluorescent film is generally produced by homogeneously applying aphosphor paste composition to a supporting substrate, followed by dryingthe phosphor paste composition. In general, phosphor paste compositionscomprise a solvent, a binder and a phosphor and selectively comprise adispersant for improving dispersibility of the phosphor.

The dispersant improves dispersibility of the phosphor, which leads to alower viscosity. Thus by improving dispersibility, it is possible toincrease the amount of the phosphor present in a given fluorescent filmand to thereby increase the packing density of the phosphor in afluorescent film. Thus the efficiency of fluorescence can be increasedover a comparative film having an equivalent thickness, but having alower packing density. Using a dispersant also permits an increase inthe stability of a paste that can be used in a printing process.

Dispersants that are surfactants include a head and a tail. The headmust have an affinity for a dispersoid to be dispersed in the dispersionmedia. The tail must have an affinity for a dispersion media capable ofdispersing the dispersoid. In addition, it is desirable to use adispersant capable of keeping adjacent phosphor particles apart fromeach other. In other words, it is desirable for the dispersant toprevent the phosphor particles from agglomerating with one another.

Commercially available dispersants for a phosphor have a monofunctionalhead generally comprise either an acidic group, or a basic or aromaticgroups, and thus can disperse only specific phosphors having an affinityfor selected functional group that are attracted to either the acidicgroup or the basic or the aromatic groups.

Accordingly, to improve the luminescent properties of display devices,there is an increasing demand to develop a novel dispersant for aphosphor that is capable of being applied to a variety of phosphors,e.g., organic phosphors, and exhibits superior dispersibility.

SUMMARY OF THE INVENTION

In one embodiment, it is desirable for a dispersant for a phosphorhaving a multifunctional head to have an enhanced affinity for thesurface of the phosphor particles and thus improve dispersability. Themultifunctional head comprises an acidic group, a basic group and anaromatic group.

The dispersant is capable of dispersing a variety of phosphors, ishomogenous and exhibits superior dispersive capabilities For phosphorsover other commercially available phosphors that do not have themultifunctional head.

A high luminance fluorescent film made using the dispersant can also beeasily processed.

In another embodiment, a display device can be manufactured, wherein thedisplay device comprises the fluorescent film that comprises thedispersant.

In another embodiment, there is provided a phosphor paste compositioncomprising the dispersant, a phosphor, and a binder solution comprisinga solvent and an organic binder.

In yet another embodiment, the phosphor paste composition comprises abinder solution comprising a solvent and an organic binder, and aphosphor.

The phosphor paste composition may comprise about 30 to about 70% byweight of the phosphor, about 0.1 to about 10% by weight of thedispersant with respect to the phosphor powder, and the balance of thebinder solution.

The phosphor paste may be used in the manufacture of fluorescent filmsthat may be used in display devices, such as cathodoluminescentdisplays, liquid crystal displays, electroluminescence displays, and thelike.

BRIEF DESCRIPTION OF THE DRAWINGS

The aforementioned features and other advantages will be more clearlyunderstood from the following detailed description taken in conjunctionwith the accompanying drawings, in which:

FIG. 1 is a ¹H-NMR spectrum of a dispersant synthesized in SynthesisExample 1 according to one embodiment;

FIG. 2 is a ¹H-NMR spectrum of a dispersant synthesized in SynthesisExample 2 according to another embodiment;

FIG. 3 a is a graph showing a comparison in the luminescent propertiesof fluorescent films produced from phosphor paste compositions preparedby mixing a polyester binder with a dispersant according to oneembodiment of the present invention, and FIG. 3 b is a graph showing acomparison in the luminescent properties of fluorescent films producedfrom phosphor paste compositions prepared by mixing a polyacrylatebinder with a dispersant according to one embodiment; and

FIG. 4 a is a graph showing a comparison in the luminescent propertiesof fluorescent films produced from phosphor paste compositions preparedby mixing a polyester binder with a dispersant according to oneembodiment, and FIG. 4 b is a graph showing a comparison in theluminescent properties of fluorescent films produced from phosphor pastecompositions prepared by mixing a polyacrylate binder with a dispersantaccording to one embodiment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The aforementioned embodiments will now be described in greater detailwith reference to the accompanying drawings.

As noted above, the dispersant comprises a multi head structurecomprises an acidic group, a basic group and an aromatic group.

In one embodiment, the dispersant is represented by Formula 1 or 2:

wherein A is an aromatic group, B is an acidic group and C is a basicgroup; a, b and c are independently an integer from 0 to about 10 withthe proviso that two or more of a, b and c are not simultaneously zero;n is an integer of 1 to about 15; and D is hydrogen, alkyl, polyester orpolyether; and

wherein A is an aromatic group, B is an acidic group and C is a basicgroup; a, b and c are independently an integer of 0 to about 10 with theproviso that two or more of a, b and c are not simultaneously zero; andn is an integer of 1 to about 15; and D is hydrogen, alkyl, polyester orpolyether.

In the dispersant of Formula 1 or 2, A is benzene, or a heterocycliccompound substituted with nitrogen (N), sulfur (S) or oxygen (O); B isselected from carboxyl (—COOH) and phosphoryl (POOH) groups; and C isselected from aliphatic amine (—NR₂) wherein R is H, CH₃, CH₂CH₃,(CH₂)₂CH₃, or (CH₂)₃CH₃, and aromatic amine (—XNR₂) wherein X isbenzene, and R is H, CH₃, CH₂CH₃, (CH₂)₂CH₃, or (CH₂)₃CH₃.

As can be seen from Formulas 1 and 2, the dispersant comprises anacidic, basic and aromatic functional groups whose ratios can beregulated to a desired level, thereby improving the affinity between oneof the groups and the surface of phosphor particles. In other words, aspecific functional group included in the head of the dispersant canhave an affinity for the surface of phosphor particles that havechemical properties similar to the specific functional group. Generally,the surface of the phosphor particles does not have a single property,but a plurality of properties one of which may be compatible with one ofthe properties of one of the functional groups disposed upon the head ofthe dispersant.

Since the dispersant described above has a head comprising multiplefunctional group, the probability of it adhering to the surface ofphosphor particles is improved. More specifically, a larger fraction ofthe dispersant can adhere to the surface of phosphor particles. Inaddition, the adhesive forces between the dispersant and the phosphor isimproved. As a result, there can be improved dispersibility for aphosphor powder within a phosphor paste composition when the dispersantis used in the composition.

In the case where a dispersant is used for a phosphor powder havinglarge differences in acidity of various phosphor particles, it isdesirable to use a dispersant that comprises a block copolymer.

The dispersant can be applied to a variety of phosphors, e.g., organicand inorganic phosphors, by controlling the ratio of the functionalgroups.

The dispersant according to one embodiment preferably has a molecularweight of about 1,000 to about 20,000.

The dispersant can be prepared by copolymerizing at least two monomersin the presence of a catalyst. The monomer is selected from benzylmethacrylate, trimethylsilyl methacrylate, (diethylamino)ethylmethacrylate, glycidyl methacrylate, or the like, or a combinationcomprising at least one of the foregoing monomers. During thecopolymerization, the structure (e.g., random or block) of thedispersant may be varied depending on the amount and addition type ofeach functional group.

More specifically, examples of preferred dispersants that can berepresented by Formula 1 include a compound represented by Formula 3below:

wherein a, b and c are independently an integer from 0 to about 10 withthe proviso that two or more of a, b and c are not simultaneously zero;and n is an integer of about 1 to about 15.

Examples of preferred dispersants that can be represented by Formula 2include a compound represented by Formula 4 below:

wherein a, b and c are independently an integer from 0 to about 10 withthe proviso that two or more of a, b and c are not simultaneously zero;and n is an integer of about 1 to about 15.

In yet another embodiment, a phosphor paste composition comprises abinder solution and a phosphor, in addition to the dispersant.

The binder solution comprises an organic binder and a solvent. Theorganic binder is used to modify the viscosity of the phosphor pastecomposition. The organic binder is generally dissolved in the solvent,and prevents damage to the fluorescent film by changing the energy ofattraction between the phosphors and the substrate, or between adjacentphosphor particles after the phosphor paste composition is dried.Examples of organic binder resins that can be used are acrylic polymers,styrenic polymers, cellulosic polymers, methacrylate ester polymers,styrene-acrylate ester copolymers, polyvinylbutyrals, polyvinylalcohols, polyalkylene oxides, polypropylene carbonates,polymethylmethacrylates, polyesters, or the like, or a combinationcomprising at least one of the foregoing polymers. The organic binder isdetermined depending on the kind of an electronic application and thetype of coating process.

Taking into consideration the kinds of the phosphor and the organicbinder and the desired physical properties of the phosphor pastecomposition, the solvent used to prepare the binder solution can beselected from commercially available solvents and mixtures thereof.There is no particular restriction as to the kind of solvents that canbe used in the phosphor paste composition, but it is desirable to usesolvents that are volatilized at 150° C. or higher.

Examples of solvents that can be used are aromatic hydrocarboncompounds, e.g., toluene and xylene; ether compounds, e.g.,tetrahydrofuran and 1,2-butoxyethane; ketone compounds, e.g., acetone,methyl ethyl ketone and cyclohexanone; ester compounds, e.g., ethylacetate, butyl acetate and butyl carbitol acetate (BCA); and alcoholcompounds, e.g., isopropyl alcohol, diethylene glycol monobutyl ether,terpineol, 2-phenoxyethanol, or the like, or a combination comprising atleast one of the foregoing solvents.

The binder solution includes about 1.5 to about 30% by weight of theorganic binder and the remainder of a mixed solvent. When the organicbinder is used in an amount less than 1.5% by weight, there maydisadvantageously occur deterioration in the quality (e.g., bindingforce) of a fluorescent film, after the phosphor paste composition isdried. Meanwhile, when the organic binder is used in an amount exceeding30% by weight, there may disadvantageously occur a reduction in theamount of the phosphor used.

The phosphor used in the phosphor paste composition of is not speciallyrestricted so long as it is used to prepare conventional phosphor pastecompositions. Particularly, there is no restriction as to the kind andcomposition of the phosphor used. Since the phosphor paste compositionis mainly used to form fluorescent films for display devices, such ascathodoluminescent displays, liquid crystal displays andelectroluminescence displays, as well as for exterior decoration anddisplay parts of electronic appliances, e.g., keypads of cellularphones, the kind and composition of the phosphor may be suitablyselected according to the kind of excitation sources used to form thedisplay devices and to excite the fluorescent films formed from thephosphor paste composition.

Specifically, commercially available red, green and blue phosphors inthe form of oxide solid solutions may be used. Sulfide and organicphosphors may be used as the suitable phosphors. The type of phosphorsdepends upon the kind of excitation sources used in the display devices.

The phosphor paste composition may further comprise at least oneadditive selected from plasticizers, leveling agents, lubricants,antifoamers and the like, so long as the physical properties of thecomposition do not deteriorate.

The phosphor paste composition may comprise about 30 to about 70% byweight of the phosphor, the phosphor being in the form of a powder; withabout 0.1 to about 10% by weight of the dispersant; the weight of thedispersant being based upon the weight of the phosphor powder, with thebalance being the binder solution.

When the dispersant is used in amounts of less than 0.1% by weight, theamount of the phosphor used is has to be increased in order to producethe same amount of luminance. The result is that the viscosity of thephosphor paste composition is increased and processing becomesdifficult. Meanwhile, when the content of the dispersant exceeds 10% byweight, the contents of the other components has to be reduced in orderto generate the same amount of luminance and there is a risk that thephysical properties of the phosphor paste composition may bedeteriorated.

By using the dispersant the content of the phosphor can be increased toabout 40 to about 70% by weight, based upon the weight of the pastecomposition. Further, the increased content of the phosphor in thephosphor paste composition contributes to an improvement in theluminance of a fluorescent film formed from the paste composition.

The phosphor paste composition can be prepared by adding the dispersantto the binder solution and adding the phosphor powder thereto.Specifically, the phosphor paste composition can be prepared inaccordance with the following procedure. First, an organic binder, suchas polyester, is dissolved in cyclohexanone as a solvent. Then, to thesolution are added a vehicle (the vehicle being another solution inwhich the binder is melted), followed by the addition of a phosphor. Theresulting mixture is homogeneously dispersed using a mill, such as a3-roll mill, to prepare the final phosphor paste composition.

In one embodiment, a fluorescent film can be produced from the phosphorpaste composition. The fluorescent film is produced by applying thephosphor paste composition to a support, such as glass or transparentplastic, to form a particular pattern thereon and firing the coatedsupport by drying and baking.

The fluorescent film can be produced by known techniques, including butnot limited to pattern screen printing, gravure roll coating, ink jet,and the like.

The fluorescent film produced from the phosphor paste compositionenables an increase in the packing density of the phosphor, animprovement in the luminance, and a relatively limited increase in theviscosity of the composition despite the increased loading amount ofphosphors, thus leading to an improvement in the processability of thefluorescent film.

The fluorescent film of the present invention can be used for thefabrication of a variety of display devices, includingcathodoluminescent displays, liquid crystal displays,electroluminescence displays, field emission displays and vacuumfluorescent displays. In addition, the fluorescent film can be used as adisplay material for exterior decoration of electronic appliances, e.g.,keypads of cellular phones. Display devices comprising the fluorescentfilm exhibit improved luminescent properties and uniform physicalproperties.

Hereinafter, the invention will be explained in more detail withreference to the following examples. However, these examples are givenfor the purpose of illustration and are not to be construed as limitingthe scope of the invention.

EXAMPLES Synthesis Example 1

The dispersant represented by the following Formula 5 can be synthesizedby the following reaction scheme 1:

i) Formation of Random Copolymer as Backbone

Methyl dimethylketene methyltrimethylsilyl acetal (1.74 grams (g), 10mmol) as an initiator, tetrabutylammonium-chlorobenzoate (0.4 g, 0.1mmol) as a catalyst and acetonitrile (3 ml) were placed in around-bottom flask under an argon atmosphere at room temperature, andstirred using a magnetic bar for two hours. To the reaction solution wasslowly added a solution of benzyl methacrylate (BMA, 6.16 g, 0.035mmol), trimethylsilyl methacrylate (TMSMA, 2.37 g, 0.015 mol) andglycidyl methacrylate (GMA, 0.71 g, 0.005 mol) as monomers intetrahydrofuran (THF, 10 ml). After stirring for 4 hours, thecopolymerization was completed to yield a random copolymer compound 1 asa backbone having (BMA:TMSMA:GMA=7:3:1 (w/w/w), with an estimatedmolecular weight of 2,500 grams/mole).

ii) Introduction Carboxyl Group into Trimethylsilyl Methacrylate

To substitute the silyl group of trimethylsilyl methacrylate in thebackbone 1 with a carboxyl group, to the TFT solution was added methanoland refluxed for 6 hours. The solvent was removed under a reducedpressure. The residue was dried in a vacuum oven for 24 hours to yield acompound 2 in the form of solid powder, where a carboxyl group isintroduced into the trimethylsilyl methacrylate.

iii) Introduction Amine Group into Glycidyl Methacrylate

To substitute the glycidyl group of glycidyl methacrylate in thebackbone 2 with an amine group, the compound 2 (2 g) was dissolved inglyme (0.5 mL). To the solution was added diethyl amine and stirred withsilica gel under a nitrogen atmosphere at room temperature for 3 hours.The reaction mixture was precipitated in ethyl ether. The precipitatewas filtered to remove the silica gel. The residue was dried in a vacuumoven for 24 hours to yield a compound 3 (a dispersant represented byFormula 5 below) as a solid powder.

The ¹H-NMR spectrum of the dispersant of Formula 5 thus synthesized wasshown in FIG. 1.

Synthesis Example 2

The dispersant represented by the following Formula 6 can be synthesizedby the following reaction scheme 2:

i) Formation of Random Copolymer as Backbone

Methyl dimethylketene methyltrimethylsilyl acetal (1.74 g, 10 mmol) asan initiator, tetrabutylammonium-chlorobenzoate (0.4 g, 0.1 mmol) as acatalyst and acetonitrile (3 ml) were placed in a round-bottom flaskunder an argon atmosphere at room temperature, and stirred using amagnetic bar for two hours. To the reaction solution was slowly added asolution of benzyl methacrylate (BMA, 6.16 g, 0.035 mmol),trimethylsilyl methacrylate (TMSMA, 2.37 g, 0.015 mol) and(diethylamino)ethyl methacrylate (DEAEMA, 0.92 g, 0.005 mol) as monomersin tetrahydrofuran (THF, 10 ml). After stirring for 4 hours, thecopolymerization was completed to yield a random copolymer compound 4 asa backbone having (BMA:TMSMA:DEAEMA=7:3:1 (w/w/w), and an estimatedmolecular weight of 2,500 g/mole).

ii) Introduction Carboxyl Group into Trimethylsilyl Methacrylate

To substitute the silyl group of trimethylsilyl methacrylate in thebackbone 4 with a carboxyl group, to the TFT solution was added methanoland refluxed for 6 hours. The solvent was removed under a reducedpressure. The residue was dried in a vacuum oven for 24 hours to yield acompound 5 (a dispersant represented by Formula 6 below) as a solidpowder.

The ¹H-NMR spectrum of the dispersant of Formula 6 thus synthesized wasshown in FIG. 2.

Example 1

A commercially available organic red phosphor powder (PKS_(—)225,UkSeung Chemical Co., Ltd., Korea) was used as a phosphor. Polyester wasused as an organic binder. 45% polyester binder in cyclohexanone(TEIKOKU INS INK 000 series) was used as a binder solution. To thebinder solution was added the phosphor powder (2 g) and a solution(0.333 g) of a 30% dispersant in cyclohexanone. The dispersant wasprepared in accordance with the Synthesis Examples while the ratio of anaromatic, acidic and basic group was adjusted to 9:1:1. The mixture wasmilled to prepare a phosphor paste composition.

The phosphor paste composition was coated onto a polyethyleneterephthalate (PET) transparent film using a doctor blade. The coatingwas dried on a hot plate at 100° C. for 10 min to produce a fluorescentfilm with a thickness of 35 μm.

Example 2

A fluorescent film was produced in the same manner as in Example 1,except that a dispersant, where the ratio of an aromatic, acidic andbasic group is 7:3:1, was used.

Example 3

A fluorescent film was produced in the same manner as in Example 1,except that a dispersant, where the ratio of an aromatic, acidic andbasic group is 5:5:1, was used.

Example 4

A fluorescent film was produced in the same manner as in Example 1,except that a dispersant, where the ratio of an aromatic, acidic andbasic group is 7:3:3, was used.

Example 5

A fluorescent film was produced in the same manner as in Example 1,except that a dispersant where the ratio of an aromatic, acidic andbasic group is 7:3:1 was used, and the basic group was bonded to a blocktype copolymer. The block type copolymer was synthesized under the samereaction conditions in accordance with the same functionalization methodas a random type copolymer, except that the addition of monomers wasperformed not simultaneously but separately.

Each type of the dispersant used in Examples 1 to 5 is summarized in theTable 1 below:

TABLE 1 Ratio (Aromatic:Acidic:Basic group, w/w/w) Binding type ofAromatic group Acidic group Basic group basic group Ex. 1 9 1 1 RandomEx. 2 7 3 1 Ex. 3 5 5 1 Ex. 4 7 3 3 Ex. 5 7 3 1 Block

Examples 6-10

Fluorescent films were respectively produced in the same manner as inExamples 1 to 5, except that a solution (molecular weight: 30,000) of37% polyacrylate in PGMEA (propylene glycol methyl ether acetate) wasused as an organic binder solution, and the thickness of the fluorescentfilms was 30 μm.

Example 11

A fluorescent film was produced in the same manner as in Example 1,except that polyester acrylate (EB657, acid value: 20 mg KOH/g, basevalue: 25 mg KOH/g, molecular weight: 1,500, SK CYTEC. Co., Ltd., Korea)was used as a dispersant.

Example 12

A fluorescent film was produced in the same manner as in Example 6,except that polyester acrylate (EB657, acid value: 20 mg KOH/g, basevalue: 25 mg KOH/g, molecular weight 1,500 grams per mole, SK CYTEC.Co., Ltd., Korea) was used as a dispersant.

Comparative Example 1

A fluorescent film was produced in the same manner as in Example 1,except that no dispersant was used.

Comparative Example 2

A fluorescent film was produced in the same manner as in Example 1,except that dispersant BYK170 containing only acidic group (BYK chemie,acid value: 11 mgKOH/g) was used as a dispersant.

Comparative Example 3

A fluorescent film was produced in the same manner as in Example 1,except that dispersant BYK161 containing only basic groups (BYK chemie,amine value: 11 mgKOH/g) was used as a dispersant.

Comparative Examples 4-6

Fluorescent films were respectively produced in the same manner as inComparative Examples 1 to 3, except that a solution (molecular weight30,000 grams/mole) of 37% polyacrylate in PAMEA was used as an organicbinder solution, and the thickness of the fluorescent films was 30 μm.

Experimental Example Evaluation of the Luminescent Properties ofFluorescent Films

To evaluate the luminescent properties of the florescent films producedin Examples 1 to 12 and Comparative Examples 1 to 6, the luminescenceintensity of each florescent film was measured on a UV luminescentdevice at a wavelength of 400 nm. At this time, the luminescenceintensity was measured using an Ocean Optics USB 100 detector.

The results are shown in FIGS. 3 a and 3 b, and FIGS. 4 a and 4 b.

As shown in FIGS. 3 a and 3 b, and FIGS. 4 a and 4 b, when comparedunder the same conditions of thickness and wavelength (i.e., 400 nm),the luminescence intensity of the florescent films (Examples 1 to 12)produced using dispersants having a multifunctional head structure wasincreased, respectively, when compared with the florescent films(Comparative Examples 1 to 6) produced using conventional dispersants orwithout using any dispersant. The graphs shown in FIGS. 4 a and 4 bdemonstrate, when compared using the same binder, that the luminescenceintensity of the florescent films produced using the dispersantcomprising both acidic and basic groups was increased, as compared tothat of the florescent films produced using the dispersant containingeither acidic or basic groups. As shown in FIGS. 3 a and 3 b, when theflorescent films comprise a polyester-based binder, the dispersants,where aromatic, acidic and basic groups are respectively used in a ratioof are respectively 7:3:1, 7:3:3, and 5:5:1, are effective in exhibitinghigh luminescence intensity. When the florescent films comprise apolyacrylate-based binder, the dispersants, where aromatic, acidic andbasic groups are respectively used in a ratio of 9:1:1, 7:3:3, and5:5:1, are effective in exhibiting high luminescence intensity. Theseresults show that the phosphor paste compositions comprising thedispersants of the present invention exhibit improved luminescenceintensity as compared to conventional phosphor paste compositions.

Although the preferred embodiments of the present invention have beendisclosed for illustrative purposes, those skilled in the art willappreciate that various modifications and variations are possible,without departing from the scope and spirit of the invention asdisclosed in the appended claims. Accordingly, such modifications andvariations are intended to come within the scope of the appended claims.

As apparent from the above description, the novel dispersant hasadvantages that it can improve the dispersibility of a phosphor pastecomposition when it is used to prepare the phosphor paste composition,and be applied to a variety of phosphors.

Since the phosphor paste composition comprising the dispersant improvesdispersibility and limits an increase in viscosity, it permits the useof a larger amount of a phosphor, thus enabling the formation of uniformfluorescent films having improved luminescent properties. Displaydevices, such as LCDs, having high luminance and excellentprocessability can be fabricated.

1. A dispersant having a multifunctional head represented by Formula 1or 2:

wherein A is an aromatic group, B is an acidic group and C is a basicgroup; a, b and c are independently an integer from 0 to about 10 withthe proviso that two or more of a, b and c are not simultaneously zero;n is an integer of about 1 to about 15; and D is hydrogen, alkyl,polyester or polyether;

wherein A is an aromatic group, B is an acidic group and C is a basicgroup; a, b and c are independently an integer from 0 to about 10 withthe proviso that two or more of a, b and c are not simultaneously zero;n is an integer of about 1 to about 15; and D is hydrogen, alkyl,polyester or polyether.
 2. The dispersant according to claim 1, whereinin Formula 1 and 2, A is selected from the group consisting of benzeneand a heterocyclic compound substituted with nitrogen (N), sulfur (S) oroxygen (O), B is selected from the group consisting of carboxyl (COOH)and phosphoryl (POOH) groups, and C is selected from the groupconsisting of aliphatic amine (—NR₂) wherein R is H, CH₃, CH₂CH₃,(CH₂)₂CH₃, or (CH₂)₃CH₃ and aromatic amine (—XNR₂) wherein X is benzeneand R is H, CH₃, CH₂CH₃, (CH₂)₂CH₃, or (CH₂)₃CH₃.
 3. The dispersantaccording to claim 1, wherein the dispersant of Formula 1 is representedby Formula 3 below:

wherein a, b and c are independently an integer from 0 to about 10 withthe proviso that two or more of a, b and c are not simultaneously zero,and n is an integer of about 1 to about
 15. 4. The dispersant accordingto claim 1, wherein the dispersant of Formula 2 is represented byFormula 4 below:

wherein a, b and c are independently an integer from 0 to about 10 withthe proviso that two or more of a, b and c are not simultaneously zero,and n is an integer of about 1 to about
 15. 5. The dispersant accordingto claim 1, wherein the dispersant has a molecular weight of 1,000 to20,000 grams per mole.
 6. A fluorescent film for a display deviceproduced from a phosphor paste composition, the phosphor pastecomposition comprising: a dispersant represented by Formula 1 or 2below; a binder solution of an organic binder in a solvent; and aphosphor

wherein A is an aromatic group, B is an acidic group and C is a basicgroup, a, b and c are independently an integer from 0 to about 10 withthe proviso that two or more of a, b and c are not simultaneously zero,n is an integer of about 1 to about 15, and D is hydrogen, alkyl,polyester or polyether;

wherein A is an aromatic group, B is an acidic group and C is a basicgroup, a, b and c are independently an integer from 0 to about 10 withthe proviso that two or more of a, b and c are not simultaneously zero,and n is an integer of about 1 to about
 15. 7. A display devicecomprising the fluorescent film according to claim
 6. 8. The displaydevice according to claim 7, wherein the display device is acathodoluminescent display, a liquid crystal display, anelectroluminescence display, a field emission display, or a vacuumfluorescent display.
 9. An article comprising the fluorescent filmaccording to claim
 6. 10. The article according to claim 9, wherein thearticle is an exterior decoration or keypad of cellular phone.